To have sexual relations while at least one of the persons involved is wearing a Snuggie. In some cases it might be easier if one of the persons' Snuggie is on backwards or if one of the persons is a little person and they can fit inside of their partner's Snuggie.

"Dude... Last night my girlfriend and I fuggied for the first time." -Guy 1

"You mean you've had a Snuggie for over a year and this is the first time you've ever gotten some action in it?" -Guy 2